Blasting for Large Commercial Structural Causing Residential Foundation Issues??

[ndalle03]

For several months now, blasting as been occurring twice a day for site work for a million + square foot facility. Recently, nearby (approximatley 1 mile or more) homeowners have noted foundation issues. It is starting to become a news story and homeowners are adamant that the foundation cracks are a result of the blasting. I've only had conversations and haven't seen the cracks in person.

I'm unaware of the type and/or size of blasting. Homeowners have told me that they can physically feel the "tremors" following the blasts. These homes are in northern Kentucky (negligible seismic activity).

Considering the blasts are occurring 1 mile away, is it likely that these structural cracks are related to the blasting? Seems unlikely to me, but I'm not too familiar with the effects of blasting. FYI, the typical foundation type in the region are poured in place concrete foundation walls with wood stud framing and brick veneer.

 

[WARose]

It's certainly possible.....but a more concrete answer can't be given without knowing more variables (like the weight of the charge).

Keep in mind (like any other type of loading): the damage effect is cumulative.

I can run some numbers for you myself, but I (at minimum) need to know what kind of poundage of explosive we are talking about.

 

[msquared48]

Depending on the strata underneath the homes, yes it is possible.

Need to involve a Geotech here...

Mike McCann, PE, SE (WA, HI)

 

[human909]

As above, almost anything is possible. However 1 mile is a pretty large half sphere of explosive shock wave....

What is more likely? The construction from a mile away cause the related issue or other causes. Or even that there the observed issues are unrelated at all.

 

[Lomarandil]

Agreed. It's within the realm of possiblity, but not definitive. Correlation =/= causation and all of that.

----
just call me Lo.

 

[ThomasH]

I would say that even if they feel "tremors" what is not necessarily an indication of damage. "Tremors" can be very small in terms of vibration levels.

Thomas

 

[Ron247]

If they are concerned, they need to get information about when new explosions are to occur. Document the existing condition shortly before the next explosion and shortly after. Document with digital photos and measurements. It is also just as important to know for sure that some areas have no defects before an explosion. Both damaged and undamaged areas need to be accurately documented.

When something like this occurs, it is human nature for people to look closely at their house. Many times, this is the first time they have ever looked closely. For that reason, they think every defect they see is new. Many times it is not. I have looked at a lot of houses following storms, subsurface mining, vibration of any kind, car impacts etc. At times there may be new damage or old damage that was made worse but in most all cases, there are some defects I am fairly are old but the Clients refuses to believe they never noticed it before. The people are not lying, but they are mistaken sometimes. In many cases, I can prove with 100% certainty the defect is old.

The pre and post explosion documentation needs to be a narrow window. It is no good to do the pre documentation today, have 2 storms occur in the next 2 weeks and then have an explosion. The same is true about having a storm following the explosion before you do the post documentation. Narrow window is needed.

 

[oldestguy]

Very likely this outfit doing the blasting has monitoring stations between it and the neighborhood. There is a wealth of information out there showing about how much vibration will cause measurable damage to most structures and it is likely the blasts are set for a much lower level of vibration at their perimeter. It takes a "hell" of a lot of displacement by the shock to cause damage. Much more than that which really seems strong to humans.

 

[miningman]

Bottom line, someone needs to explain to the complaining homeowners that it is 99% likely they will be wasting their time and money looking for financial compensation or cessation of blasting. All blasting contractors have been down this road more than once and know how to refute frivolous claims.